On the TD12 I finally figured out where to go to change the backing track volume (you have to change each part but its the only way as the kit sound wont go louder without the backing doing so too.

However, in the settings screen next to each fader for the instruments in the backing track, there's a lock icon and I cannot figure out how to actually move the faders so I looked at the manual and checked to see if there was any special button combo that was required but it just says: